The present disclosure relates to image processing apparatuses, image processing methods, and image processing programs.
An image pickup device having a CMOS image sensor, such as a video camera or a digital still camera, is used for taking pictures under various environments such as indoors, outdoors, during the day, and during the night. In accordance with changes in the received light, an electronic shutter that controls a charge accumulation period in the CMOS image sensor sets the sensitivity at an optimum value by adjusting the exposure time.
To widen a dynamic range by using the CMOS image sensor, there are a method by which the exposure time is adjusted by releasing the electronic shutter at high speeds, a method by which pictures of a plurality of frames are taken at high speeds and the imaging results are superimposed, and other methods.
In Japanese Unexamined Patent Application Publication No. 2008-99158, a technology that makes it possible to acquire a linear signal with a high signal-to-noise ratio without narrowing the normal saturation level in low illumination and makes it possible to widen a dynamic range while realizing a satisfactory signal-to-noise ratio in a linear region for incident light whose level is higher than or equal to the normal saturation level has been disclosed. In this method, as shown in FIG. 9, for example, the time between t4 and t5 is set at 1/16 of the exposure time t0 to t6 of one frame. Then, the electric charge more than or equal to the accumulated electric charge dM is reset at time t4, exposure is performed again between t4 and t5, and the electric charge more than or equal to the accumulated electric charge dM is reset at time t5. Based on the amount of electric charge d3−dM exposed between t4 and t5 and the amount of electric charge d4 exposed in the exposure time (t0 to t6) of one frame, the amount of electric charge which is obtained by exposure in one frame is calculated. Hereinafter, this method is referred to as the water gate method.